91991861 has 8 divisors (see below), whose sum is σ = 99142680. Its totient is φ = 84851712.

The previous prime is 91991839. The next prime is 91991891. The reversal of 91991861 is 16819919.

It can be written as a sum of positive squares in 4 ways, for example, as 24850225 + 67141636 = 4985^2 + 8194^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 91991861 - 2²² = 87797557 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91991891) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 32345 + ... + 35073.

It is an arithmetic number, because the mean of its divisors is an integer number (12392835).

Almost surely, 2^91991861 is an apocalyptic number.

It is an amenable number.

91991861 is a deficient number, since it is larger than the sum of its proper divisors (7150819).

91991861 is a wasteful number, since it uses less digits than its factorization.

91991861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5335.

The product of its digits is 34992, while the sum is 44.

The square root of 91991861 is about 9591.2387625374. The cubic root of 91991861 is about 451.4224307073.

The spelling of 91991861 in words is "ninety-one million, nine hundred ninety-one thousand, eight hundred sixty-one".